1. Field of the Invention
The invention relates to fixed ratio traction roller transmissions in which the contact forces applied to the traction surfaces which are in engagement with each other for the transmission of movement are dependent on the torque transmitted through the transmission.
2. Description of the Prior Art
Traction roller transmissions in which large contact forces are applied to prevent slippage of the rollers are described for example by Harold A. Rothbart in "Mechanical Design And Systems" Handbook, pages 14-8 and 14-9, McGraw-Hill, New York, 1964. In the relatively simple arrangements of FIGS. 14.6 and 14.7 wherein the outer rings are slightly undersized to compress the roller arrangements, the surface pressure on the traction surfaces is always the same; that is, it is always high independently of the torque transmitted through the transmission. Various transmission arrangements are also known in which the contact pressure of the traction surfaces is dependent on the size of the torque transmitted through the transmission, for example, as in those shown on page 14-8 of said handbook. A transmission of this type in which the forces with which the traction rollers are held in engagement with one another is shown in U.S. Pat. No. 3,610,060. A transmission which includes Belleville-type springs on the sun roller or the traction ring surrounding the planetary rollers is disclosed in the present inventor's earlier U.S. Pat. No. 4,215,595.
In such a traction roller transmission, a sun roller is supported by one of coaxial input and output shafts and traction rollers are disposed around the sun roller, while a traction ring structure surrounds, and is in contact with, the traction rollers. One or both of the traction ring and sun roller structures include a plurality of Belleville-type spring rings arranged between means for compressing the spring rings so as to cause engagement of the traction rollers with the sun roller and the traction ring structures. In an arrangement according to the present inventor's earlier application Ser. No. 281,983, the radial spring ring surfaces in engagement with the traction rollers are rounded to reduce wear of the roller surfaces.
Transmission of large torques however requires large contact forces which, with a relatively small contact area, results in relatively high wear. In addition, the Belleville springs' radial surfaces must be manufactured within very small tolerances.